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In Java, a finally block encloses the statements that are always executed whether an exception was thrown by the program or not.






A finally block can be defined at either of two places -



• A finally block can be defined right after the try-catch block.
• A finally block can be defined right after the try block(if catch block is not defined)

Conditions when a finally block runs -

• If an exception is not thrown out of try block, finally block still runs.

//Java - Finally Block
 
 
class A
{
public static void main(String... ar)
{
try
{
	A ob = new A ();
}
catch(Exception e)
{
	System.out.println( "Exception caught"+e);
}
finally
{
	System.out.println("A finally block is executed irrespective of an exception is thrown or not");
}

}
}
 





Output -




A finally block is executed irrespective of an exception is thrown or not








If an exception thrown by try block is caught by catch block, the finally block still runs.




//Java - Finally Block


class A
{
public static void main(String... ar)
{
try
{
	Integer i = new Integer("One");
}
catch(Exception e)
{
	System.out.println("Exception caught - "+e);
}
finally
{
	System.out.println("A finally block is executed even after an exception is caught in the catch-block");
}

}
}





Output -




Exception caught - java.lang.NumberFormatException: For input string: "One"
A finally block is executed even after an exception is caught in the catch-block



An exception of type NumberFormatException is thrown when an illegal string is passed to the constructor of wrapper class, Integer, which can't be converted to an Integer object. A catch block is declared with Exception class, which is a superclass of every exception class in Java. Hence, the catch block catches the exception NumberFormatException and the finally block runs despite the exception being caught in the catch block.




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If an exception thrown by the try block is not caught by the catch block, the finally block still runs.




//Java - Finally Block


class A
{
public static void main(String... ar)
{
try
{	
	A ob = null;
	System.out.println(ob.toString()); //calling toString() on null reference throws NullPointerException
}
catch(ArithmeticException e)
{
	System.out.println("Exception caught - "+e);
}
finally
{
	System.out.println("A finally block is executed even after an exception is not caught in the catch-block");
}

}
}





Output-




A finally block is executed even after an exception is not caught in the catch-block
Exception in thread "main" java.lang.NullPointerException
        at A.main(Ex13.java:8)



In the try block, calling toString() method on a null reference throws a NullPointerException, the catch block is declared with a different exception of type ArithmeticException, hence the NullPointerException is not caught in the catch block. Despite this, the finally block still runs and exception is thrown after executing the finally block.






If an exception is thrown by try block and a catch block is not defined, but the finally block is defined, the finally block runs.




//Java - Finally Block


class A
{
public static void main(String... ar)
{
try
{
	A ob = null;
	System.out.println(ob.toString());
}
finally
{
	System.out.println("A finally block is executed in the absence of catch-block, when exception is thrown.");
}

}
}





Output-




A finally block is executed in the absence of catch-block, when exception is thrown.
Exception in thread "main" java.lang.NullPointerException
        at A.main(Ex13.java:8)








If an exception is not thrown by try block and a catch block is not defined, but a finally block is defined, the finally block runs.




//Java - Finally Block

class A
{
public static void main(String... ar)
{
try
{
	A  ob = new A();
}
finally
{
	System.out.println("A finally block is executed in the absence of catch-block, when exception is not thrown.");
}

}
}

Output-

A finally block is executed in the absence of catch-block, when exception is not thrown.

So, a finally block(when defined) always runs, no matter if an exception is thrown or not.

Use of finally block

Objects may hold references to the system resources like memory, files, database which need to be released in a timely fashion when they are no longer needed. Hence, a finally block usually contains a clean-up code i.e. code to release any of such resources that were referenced or locked in the try block.

Example of a finally block

//Java - Finally Block


import java.io.*;

public class Finally
{

public static void main(String... ar)
{

FileWriter fileWriter = null;
try
{
	File file = new File("D:\\File.txt");
	fileWriter = new FileWriter(file);		//creating a file
	fileWriter.write("Hello Java");			//writing data to a file
	fileWriter.flush();				//flushes the data to a file
}		//try block ends

catch(IOException e)
{
	e.printStackTrace();
}		//catch block ends

finally
{
	try
	{
		fileWriter.close();		//cleaning up the resources i.e. closing an opened file.
	}
	catch(IOException e)
	{
		System.out.println(e);
	}
}		//finally block ends

}		
}		

This program creates a text file named "File" in D drive and writes a string Hello Java to it. Here we have used finally block to run the clean-up code i.e. by calling close() method to close the stream, after the data is flushed to the file.

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